libfat/open.c

   1 /* ----------------------------------------------------------------------- *
   2  *
   3  *   Copyright 2004-2008 H. Peter Anvin - All Rights Reserved
   4  *
   5  *   This program is free software; you can redistribute it and/or modify
   6  *   it under the terms of the GNU General Public License as published by
   7  *   the Free Software Foundation, Inc., 53 Temple Place Ste 330,
   8  *   Boston MA 02111-1307, USA; either version 2 of the License, or
   9  *   (at your option) any later version; incorporated herein by reference.
  10  *
  11  * ----------------------------------------------------------------------- */
  12
  13 /*
  14  * open.c
  15  *
  16  * Open a FAT filesystem and compute some initial values; return NULL
  17  * on failure.
  18  */
  19
  20 #include <stdlib.h>
  21 #include "libfatint.h"
  22 #include "ulint.h"
  23
  24 struct libfat_filesystem *
  25 libfat_open(int (*readfunc) (intptr_t, void *, size_t, libfat_sector_t),
  26             intptr_t readptr)
  27 {
  28     struct libfat_filesystem *fs = NULL;
  29     struct fat_bootsect *bs;
  30     int i;
  31     uint32_t sectors, fatsize, minfatsize, rootdirsize;
  32     uint32_t nclusters;
  33
  34     fs = malloc(sizeof(struct libfat_filesystem));
  35     if (!fs)
  36         goto barf;
  37
  38     fs->sectors = NULL;
  39     fs->read = readfunc;
  40     fs->readptr = readptr;
  41
  42     bs = libfat_get_sector(fs, 0);
  43     if (!bs)
  44         goto barf;
  45
  46     if (read16(&bs->bsBytesPerSec) != LIBFAT_SECTOR_SIZE)
  47         goto barf;
  48
  49     for (i = 0; i <= 8; i++) {
  50         if ((uint8_t) (1 << i) == read8(&bs->bsSecPerClust))
  51             break;
  52     }
  53     if (i > 8)
  54         goto barf;
  55     fs->clustsize = 1 << i;     /* Treat 0 as 2^8 = 64K */
  56     fs->clustshift = i;
  57
  58     sectors = read16(&bs->bsSectors);
  59     if (!sectors)
  60         sectors = read32(&bs->bsHugeSectors);
  61
  62     fs->end = sectors;
  63
  64     fs->fat = read16(&bs->bsResSectors);
  65     fatsize = read16(&bs->bsFATsecs);
  66     if (!fatsize)
  67         fatsize = read32(&bs->u.fat32.bpb_fatsz32);
  68
  69     fs->rootdir = fs->fat + fatsize * read8(&bs->bsFATs);
  70
  71     rootdirsize = ((read16(&bs->bsRootDirEnts) << 5) + LIBFAT_SECTOR_MASK)
  72         >> LIBFAT_SECTOR_SHIFT;
  73     fs->data = fs->rootdir + rootdirsize;
  74
  75     /* Sanity checking */
  76     if (fs->data >= fs->end)
  77         goto barf;
  78
  79     /* Figure out how many clusters */
  80     nclusters = (fs->end - fs->data) >> fs->clustshift;
  81     fs->endcluster = nclusters + 2;
  82
  83     if (nclusters <= 0xff4) {
  84         fs->fat_type = FAT12;
  85         minfatsize = fs->endcluster + (fs->endcluster >> 1);
  86     } else if (nclusters <= 0xfff4) {
  87         fs->fat_type = FAT16;
  88         minfatsize = fs->endcluster << 1;
  89     } else if (nclusters <= 0xffffff4) {
  90         fs->fat_type = FAT28;
  91         minfatsize = fs->endcluster << 2;
  92     } else
  93         goto barf;              /* Impossibly many clusters */
  94
  95     minfatsize = (minfatsize + LIBFAT_SECTOR_SIZE - 1) >> LIBFAT_SECTOR_SHIFT;
  96
  97     if (minfatsize > fatsize)
  98         goto barf;              /* The FATs don't fit */
  99
 100     if (fs->fat_type == FAT28)
 101         fs->rootcluster = read32(&bs->u.fat32.bpb_rootclus);
 102     else
 103         fs->rootcluster = 0;
 104
 105     return fs;                  /* All good */
 106
 107 barf:
 108     if (fs)
 109         free(fs);
 110     return NULL;
 111 }
 112
 113 void libfat_close(struct libfat_filesystem *fs)
 114 {
 115     libfat_flush(fs);
 116     free(fs);
 117 }